Communication systems allow users to communicate with each other over a communication network e.g. by conducting a call over the network. The network may be, for example, the Internet or public switched telephone network (PSTN). During a call, audio and/or video signals can be transmitted between nodes of the network, thereby allowing users to transmit and receive audio data (such as speech) and/or video data (such as webcam video) to each other in a communication session over the communication network.
Such communication systems include Voice or Video over Internet protocol (VoIP) systems. To use a VoIP system, a user installs and executes client software on a user device. The client software sets up VoIP connections as well as providing other functions such as registration and user authentication. In addition to voice communication, the client may also set up connections for communication modes, for instance to provide instant messaging (“IM”), SMS messaging, file transfer and voicemail services to users.